Ballistics testing instrument



June 2, 1953 R; l.. PIGFQRD 2,640,355

BALLISTICS TSTING INSTRUMENT Filed April 14, 1950 6 Sheets-Sheet l Ember?. L. Pigfnr'li June 2, 1953 R. L. PIGFORD I v 4 *2,640,355

BALLTSTICS TESTING INSTRUMENT Filed April 14. 1950 6 Sheets-Sheet v2 Ruh ETT L Pigfmi June 2, 1953 R, L, PlGFORD 2,640,355

BALLISTICS TESTING INSTRUMENT Filed April 14, 1950 6 Sheets-Sheet 5 'June 2, .1953 R. L.. PIGFoRD 2,640,355

, BALLISTICS TESTING INSTRUMENT Filed April 14, 1950 6 Shees-Sheet 4 sa [80, 26 Q 4? T .ae .10.29- ,4. N9-wb vv m- ]U T261 s/I Tw l aan M, li @l a 252726 K9/bg I 37 gwvQ/HM gRuh Eer-'. L Pigfnrli June 2,19s3 R. L. PIGFRD 4 2,640,355

BALLISTIcs TESTING INSTRUMENT Filed April 14. 1950 8 Sheets-Shet 5 ffm @MM/ww June 2, 1953 R. L. PIGFORD BALLISTICS TESTING INSTRUMENT Filed April 14, 1950 6 Sheets-Sheet 6 f5.4 J2 @oa ful Irc Patented June 2, 1953 BALLISTICS TESTING INSTRUMENT Robert L. Pigford, Newark, Del., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Application April 14, 1950, Serial No. 155,909

19 Claims.

This invention relates to machines for testing the ballistic characteristics of spinning projectiles. The determination of the numerous variables which affect the performance of projectiles in night, particularly those of the liquidnlled chemical type, is dinicult. Computations based on theory alone, while helpful, are eX- ceedingly complex and often unreliable in the prediction of actual performance. It is also possible to make quantitative determinations of the period of yaw near the gun. However, the motion of the projectile at this location is of minor interest. The principal quantities which must be determined for accurate prediction are range and deviation of a given projectile from the vertical plane of nre. However, significant measurements of range and deflection are dinicult to obtain because they require statistical analysis of a large number of trials or experiments and, particularly in the case of projectiles of larger calibers, are

very costly.

For the foregoing reasons, the most practicable method of determining the night characteristics of projectiles are laboratory investigations under carefully controllable conditions and highly accurate measurements. rThis is true for liquid nlled projectiles, such as those of the chemical type, as well as for those of the solid type.

It is therefore the general object of my invention to provide a testing machine in which a fullsize projectile closely simulating the actual projectile in size, weight, location of center of gravity, and moment of inertia, can be mounted, spun at speeds closely equal to the actual speed of spin of the corresponding projectile in night.

More particularly, it is an object of the invention to mount the simulated projectile for universal angular movement about transverse axes through its center of gravity while spinning, and to apply external forces to the universally mounted spinning projectile representing and closely simulating the actual aerodynamic forces which act on the real projectile in night.

A further object is to closely simulate the conditions existing during actual night of the projectile occurring along a curved trajectory by applying an overturning moment to the spinning simulated projectile and causing the line of action of the applied moment to rotate about the projectiles center of gravity at a rate equal to the angular velocity of the tangent to the trajectory of the corresponding real projectile.

A still further object is to provide a precision instrument wherein means are operable to simulate the condition where the projectiles axis does Lif) not follow the tangent to its trajectory as this tangent turns during night, by continuously angularly moving the device applying the external force to the simulated projectile to thereby correspondingly angularly move the line of action of the thrust exerted thereby.

Another object is to provide an instrument of the type mentioned wherein the aforesaid overturning moment can be variedduring the investigation of the performance of a proposed projectile to represent the condition caused principally by decrease in the velocity of night as the projectile approaches the vertex or Zenith of its path.

Still another object is to provide an instrument of the type identined which is of value in testing and determining the arming and operating characteristics of the fuzes of rotating projectiles.

-A further object is the provision of an instrument in which the angular position, speed of rotation, and rate of angular movement of the simulated projectile can be recorded and subsequently determined with a high degree of accuracy.

Another object is to provide a night-simulating and projectile-testing instrument which is rugged, reliable and highly accurate in the determination of characteristics which will enable reliable prediction of the night performance of the corresponding actual projectile.

Other objects and advantages of the invention will occur-or be obvious to those skilled in the art after a study of the following specincation in connection with the accompanying drawing, wherein:

Figure 1 is an elevational view of the entire instrument.

Figure 2 is an elevational view as seen from the left in Figure 1, portions of the supporting frame being broken away.

Figure 3 is a sectional elevation as indicated by the line 3 3 of Figure 1.

Figure 4 is a sectional plan view taken in a plane indicated by the line 4 4 of Figure 3.

Figure 5 is a sectional detail view to an enlarged scale taken in a plane identied by line 5 5 of Figure 4 and showing the bearing construction by which the rotor casing is journaled in the gimbal ring.

Figure 6 is a detail sectional view to an enlarged scale of a portion of Figure 3, showing one of the bearings by which the gimbal ring is mounted and by which air under pressure is conducted to the interior of the gimbal ring to spin the rotor.

Figure 7 is a detail elevation of the power drive A second series of tangential holes 33h through the wall of casing 33, lead from chamber 32. The holes 33h are oppositely directed from holes 33a and, when supplied with air under pressure, form jets impinging on pockets 39a to brake the rotor and bring it quickly to rest.

Pipe I5 is connected by exible tubing with a source of air under pressure, not shown. A port I1c from fitting I1 to pipe section 2|, conducts air to fitting I8, through port 2Gb, and thence to chamber 31, as previously described. On the other hand, a port I 9a from fitting I9 leads into pipe section 2 Ib and thence to fitting 20, thence through ports a and 26d, to chamber 32, as also previously described.

An air pipe 34, Figures 2, 3 and 4, corresponding to pipe I5, has an external projecting portion adapted for connection with a flexible tube, not shown, in turn connected with the source of air under pressure. Conveniently located valves (not shown) in each of the pipe connections leading to tubes I5 and 34, respectively, enable the rotor to be spun or rapidly brought to' rest, as desired. Furthermore, by means of a stroboscopic speed indicator, subsequently described, the air pressure to pipe I5 may be regulated so that the rotor spins at a speed closely equal to the speed of rotation in flight, of the actual projectile which the rotor simulates. From Figure 5 it will be noted that the clearance between band 1 39 and casing 33, is small.

The casing 33 is a hollow, generally cylindrical element having a nose cap 4I riveted or bolted thereto. This cap has a stub shaft 42 secured in its central aperture and carries a ball 42a integral with its outer end. The lower end of casing 33 is closed by a cup 43 having a circular recess to accommodate an antifriction bearing 44. Cup 43 also has a depending reduced portion 43a to which a lower bearing is aiixed.

The rotor 38 and its turbine ring 39 have previously been mentioned. This rotor is modified in size and shape to correspond with the size, shape, weight, and moment of inertia, of the actual projectile whose ight characteristics it is desired to determine. Departure from precise duplication with the actual projectile involves, generally, 1) the provision of a central circular depression 38a at the nose of the rotor to provide a seat or recess for antifriction bearing 46, (2) the attachment of turbine ring 39 and (3) the provision of portions depending from part 41 closing the lower end of the rotor. These last-mentioned portions include a short depending stub shaft 41a which has a smooth fit within bearing sleeve 48. Sleeve 48, in turn, passes through the inner race of antifriction bearing 44 and has a flanged upper end resting on this race. See Figure 3. The lower end of sleeve 48 has a smooth t within a sleeve whose lower end, in turn, fits an upwardly-facing depression in a cup or nut 45. See Figure 16. A threaded shaft 49 has a smooth upper end pinned within a bore in shaft 41a and passes with threaded engagement through central apertures in sleeve 48 and cup 45. The upper end of sleeve 55 bears against the lower surface of the inner race of bearing 44 and by turning nut 45 on shaft 49, sleeve 55 is forced upwardly to take up any axial play between its upper end, the inner race of bearing 44, and the anged upper end of sleeve 48.. Since shaft 49 is pinned to shaft 41a the rotor is held against axial movement relatively to casing 33. The lower end of cup 45 is formed to receive a wrenchF ,A central lug 45a has a threaded aperture receiving a screw 56 which acts to rigidly secure a magnet 5I of Alnico to the cup. Thus shaft 49, sleeves 48 and 55, cup 45 and magnet 5I, rotate as a unit with rotor 38. symmetrically disposed apertures 51 are provided in plug 41, each closed by a removable screw 58 to enable the rotor to be filled with liquids or fluent material having the same properties, namely, specic gravity and viscosity, as those used to lill the actual projectile.

A rod 50 depends from casing 33 and carries a small electromagnet 52 in cooperative relation with magnet 5I so that, as rotor 38 spins, an alternating E. M. F. of the same frequency as the speed of the rotor, is induced in the electromagnet and utilized to determine rotor speed in a manner subsequently explained. Casing 33 has two` sets of holes 53 and 54 equally-spaced above and below ring 26 to discharge spent air. These holes are arranged so that there is no net external moment on the casing due to reaction of the air emerging therefrom.

In accordance with the principles and purpose of may invention, means are provided to exert a thrust on the nose or forward end of the casing 33 to simulate by a single force, the forces exerted on the actual projection in flight by air resistance. In the model shown, this means includes a bail generally identified by the numeral 59. This bail is built up from parts including upwardly and inwardly-extending arms 60 and 6l rigidly united intermediate their ends by a ring 62 bolted at diametrically opposite locations to anged projections 69a and Sla, Figure 3, and as shown in detail for arm 69 upon Figure 15. Arms 30 and 6I are journaled on liners 40 and i2, respectively, whereby the bail may be swung about axis 23.

At the top, arms BIJ and 3l have their ends bent inwardly and rigidly connected by a second ring 64, Figure 9, having diametrically opposite anged portions 64a bolted as at 55 to the mating flanges formed upon the ends of arms 60 and 6I. Diametrically opposite lugs 64b and 64o, Figure 3, depend from ring 64 and carry aligned bearings defining a normally horizontal axis parallel with axis 23. A small gimbal ring 66 has aligned trunnions 65a and 66h projecting therefrom and journaled in the respective lugs 64b and 64e.

A collar 61 is journaled by bearings 19 and 1I in ring 66 for pivotal movement about an axis 69 at right angles to axis 68. This collar has an air cylinder 12 rigidly mounted therein. A piston, not shown, iits cylinder 12 and is connected with a rod 13, Figure 3, which passes through a cap 14 threaded upon the lower end of the cylinder. A nut 15 is threaded upon the lower endA of rod 13 and has a generally hemispherical .cavity tting ball 42a. By this construction, as air under pressure is admitted to cylinder 12 above the piston therein, nut 15 is urged` downwardly and exerts a force on ball 42a. This force is constant for angular positions of the casing 33 and of bail 59, relatively to frame I, so long as the air pressure in cylinder 12 remains constant. The force thus applied is as near as possible in value to the air resistance encountered by the actual projectile in flight and can be maintained constant with constant air pressure in cylinder 12, or varied to simulate conditions caused by decrease in velocity of the projectile. By swinging bail 59 about the axis 23, it is possible to simulate the conditions occurring along a curved trajectory of an actual projectile since the line of action of I the. Germaine.fefsaag; bee-retardement the.. center orggrayitfeofthegsimuiated shellat arate'.. egual i. te4 fthe angular; velocitJ1 of .a;Qtaafigent.. .to the...actiialltrajetbr If lth`sp'inn'in` 'axisi Iof*` the actual .projectile 4dees n Parallelle-i0. the. tangent .te-Cheftraar S. this tangent .turnsl th fresu4 antfwind @resistancefis A. app d. Ato the pro'j'etileslncsge along aflinem k. ingso'mex. angle. .with the l'or'igitiudli` i a1 ef. proectile. Such a onditionisa lated-bathe,.presentinstrumenth One, end l of lchannel. ,'16 ,.projetsioutwardly from, 25r

its" horizontal. and, has..Setured'theret-a.Seton@ downvuard1y-7'f`acngchannellsection ,11 v forminfg a., base ,foraonstant-'torque variablespeed -motor.. 'I3-:ot I fra'etional` hors'epqwer.. This .,IIltOr is` d'- rectll.connected`by a iexiblecoupling A"I9, with a` 0k threadedY shaft.. 8g.. jouririaledS inl self-aligning, roller bearing. .pi1low.z blacks "8 I land 82y `,boltjedgto.. U :shapedbrackets `and.Btl,irvespectiv`ely. These braelzets` are secunecl,v tofgthesides. of .channel '16,'` as clearlyshown' at Figure 1.8. forbracket,

An .elongated lstraigl'1t'- track or guide 85. is se.- cured as by screwsr Figure `8, centrally' of channel 76.' A nut o'r rider 85 has threaded .engagement with shafty 8g.. and..r includes downwardlygextending ng'ersciand Slb, embracing opposite sides of the' track y and .aroller'xfl journaled. between. the lingersv on.. ahorizontal axis. and riding upon the, topof the; track. 'In this., manner, the nutY or rider .8.6 ispreventedfrom.. rotating andis translated, with yWifi?.1ittle,. f1 ric A tion,` in response toA rotation of shaftbymoton 18. A. Spacerstrip BSwand arnoili.pans8lLtocatch any. excess lubricant, are. interposed betiiv'eenz track meriibrl .and hannl 16.

As best shown in Figures 2, 3, 7 and8,Z a. pair of, axally-spaced r parallel legers 90,.` and 9.! are rigidly, attached.. as bybolts .EL to the arm. BQ, ofy I. bailv 5.8,. to.. extend dwergrdm frem`A axis... 23- These leversV have .cggextensive `slots 93; Figure .'7 in. their .lower ends,V radial Lof axis..23. Aligned7 pianse s@ and. stehend. from 'theiespeetive' sides; ofv A nutv 86. Guide. blocks. such as,'96,` Fjigureg '7, are journaled on .the respective pintles r`and have straightparallel sigleseach tting Within acvorrespondingone ofthe Slots 93 of llk'evenslandjll Washers il? andl98 are mounted upon the respectivepintlesand spanthe slots 9.35:. Thesewa'shers, aref heldin place by,.c otter pins.and.preventexr @lessive axial y.mov.ementy of. thek guide `bloclrsupon thepintles, bythe construction just described, rotation I'o f motorfl effects pivotal moyement of bail 5.9V about aris '23, at an angular.. velocity, which is proportional to thehsquare ofthe cosine which ther bailm'akes with the verticallane. through axis'ZlS, i" b ,-0

Thus, let c=the vertical distance-.from]axis1 23W tothe, axis of screwf. (aiconstanta of,` the instrument) TEIL P Se offrriotorlsfa enstsntforanmeiren.

esta@ :Denen ofrhrads..off.hai 8@ @..Csznsaaet sind senses/erectil i H=ltheang`1e$which`bail 59 .make5 with theverti.-

cal at any given instant Then the total displacement of nut 86 ufrom central position at time t is rpt, and

In the machine shown, the parts are so dmensioned 'thatlbail 59 has a! total `movement of 45to each side of the verticalplane through axisV switches areconnected in .the circuit of motor '181 to automatically open the same and stop`fthe` motor when the bail reaches its limits of angular movement. As. shown in Figure `8,` switch 99) is mounted on a bracket [Ell bolted to bearing bracket 34. The other switch |90, is mounted in an identical manner. on bearing bracket 83. An

oiler 02 is threaded into rider lfor lubricating' its threads and those of shaft 85.3.

The .arm 6l of bail 59 has'a pin m3 ixed thereto in position below axis 23. This pin has one end of a coil spring lllfsecuredthereto.

yoke 105, Figures 1 and 2, carriedby a bolt IBB.

The' bolty passes through ahole ina bracket. |071` secured to andV extending frombrace member. 6.' Nuts threaded on the bolt on opposite,s dsf;l

the, bracket maybe adjusted to, vary the y tension in-the springhwhich acts to urgeuthe bail into vertical position when displaced therefrom,byV op;V eration orb-motor 18. asis obvious from inspec; tion or Eisma 1,

leerden-w centrali@.Cylinder foci-,13). and

T5.; .33: @nel t9. eesitirel., Resinas the. parte.

The other end of .the spring is fixed to one end of a` andere prior to the beginning of a test run so that the spin axis of rotor 38 is in alignment with rod 13 and both are in the vertical plane of bail 59, that is, the vertical plane through axis 23, I have provided cylindrical protuberances 60h and 3|?) on the upper ends of the respective arms of bail 59 which protuberances are aligned when the bail is assembled. Confining attention to bail arm 60, the protuberance 60h has an air cylinder |08 slidably fitting therein and which may be given a slight axial adjustment relatively to the arm by a screw |09 loosely passing through the aperture in a lug integral with cylinder |08, and threaded into an aligned bore in a lug depending from the protuberance.

A piston, not shown, ts cylinder |08 and has aligned rods projecting centrally from its forward and rear faces. not shown, has a clamp member secured to its forward end. The forward face of the clampy member is arcuate or Il-shaped, to t about cylinder 12 when forced thereagainst by movement of the piston assembly to the right, as the parts are viewed upon Figure 3. Such movement is opposed by the rod i I I secured to the piston and having a spring ||2 thereabout and acting 'between the adjacent surface of arm 60 and an abutment i I3 on rod I to urge the clamp member ||0 into the retracted position shown upon Figure 3. Compressed air to force the piston to the right to eiect engagement of member I I E with cylinder 12, is supplied by way of a iiexible hose, not shown, connected with a supply opening ||4. The clamping means on arm 6| may be a duplicate of the one just described so that, in addition to protuberance Bib, it will be sufficient to identify cylinder |15, adjusting screw IIS, clamp member lll, spring IIB and pistotn rod I I9. Connection with a source of air pressure is made by exible hose connected to supply 4opening I2. Any suitable means may be provided to prevent rotation of the pistons and rods Within the cylinders. For example, rods III and 9 may be non-circular and t a correspondingly-shaped passageway in the arms. The permissible stroke of each of the pistons is so adjusted that when each is forced inwardly against the head of its cylinder, clamp members ||0 and I|1,will clamp cylinder 12 and rod 13 in alignment with the spin axis of rotor 38, the axis common to all then being vertical and normal to axis 23. The pressure supply to inlets I I4 and |20 may be from the same source as that used to drive rotor 38, either direct or through a pressure-reducing valve, not shown. 1n any event, when air is admitted to the cylinders |08 and ||5, clamp members III] and ||1 are forced inwardly to centralize and align the cylinder 12 and casing 38. On release of air pressure, springs ||2 and IIB act to move the clamp members to the release position shown upon Figure 3.

In order to record the motion and position of the simulated shell at any time during a test, an optical system is provided for affording a photographic record. For this purpose, four brackets to the ends of angle member |26, likewise bolted to horizontals 4 at the side of the rotor opposite member |25. Each of the Ibrackets mentioned includes a at base for bolting to the vertical face of the angle, and a tubular vertical portion.`

The forwardly projecting rod,l

Four identical pillars or columns |21, |28, |29 and |30, two of which are clearly shown in Figure 1, have lower vertical portions each fitting within the tubular portion of a respective bracket and secured therein in any desired manner. The upper end of each column is bent in the form of an arc as clearly shown upon Figure 1. The upper end of each column terminates in an integral head such as I29a shown in detail upon Figures l2 and 13. Each head has a transverse bore such as |3|, Figure 13. The assembly is such that the heads of columns |21 and |28 which form a pair, have their bores aligned. Likewise, the heads of columns |29 and |30 which form another pair, have their bores aligned. A unitary frame for supporting the light-sensitive recording sheet or strip |31 consists of a pair of spaced parallel tubes of which one, identied at |32, is shown in Figure 12, connected by spaced parallel arcuate straps or bars |38 and |33, Figure 3 having their ends welded to the ends of the tubes. The tubes |32 are of a length to fit between the heads of the columns of a respective pair. A rod |34 is then passed through the aligned bores in the tube and heads, and, in conjunction with nuts |33 threaded on each end of the rod, rigidly secures the parts together. The straps or bars |38 and |39 may be secured together at a number of spaced points therealong (shown as three in the machine illustrated) by a construction shown at Figure 3. Thus, angle brackets |40 and |4| are b-olted to the under side of straps |33 and |39, respectively, and have their vertical arms connected by a spacer rod |42 in a manner obvious from inspection of Figure 3. It should lbe noted, referring to Figure 1, that straps |38 and |39 have their centers of curvature in axis 23, that is the pivotal axis of bail 59.

Each of the heads of columns |21 to |30, carries a screw |35, shown in detail in Figures 12 and 13 for head |29a. A paper-clamping bar |42 has apertures in its ends fitting over the screws |35 of a respective pair of heads. This bar is longitudinally grooved. A second clamping bar |43 is apertured to receive screws |35 and has a rib adapted to fit within the groove of lbar |43, as clearly shown upon Figure 13. The strip of photographic paper |31 may then be passed over and in contact at its edges with straps |33 and |39, and secured at its ends by being passed between the clamping 4bars |42 and |43 and turning .down nuts |44 threaded upon the respective screws |35. The recording paper may be in the form of a roll and, after each test or series of tests, a new section may be moved into position by loosening nuts |44 and clamp bar |43, drawing a section of fresh or unexposed paper into position and again tightening nuts |44.

For making a record of the movement of the simulated shell upon paper |31, I have provided a flash lamp projector and circuit control for making a series oi light spots upon the paper at equal time intervals. The projector per se is shown generally upon Figures l and 3, and in sectional detail upon Figure 11. It comprises a support in the form of a special cap 12a for air cylinder 12 and has an upward extension 12b, Figure 11, about which there fits the lower end of projector tube |45, secured in place by screws "'sa'ljtled i'efli y v isss'efi' elecftrodeso the lainpandQat thev4 saine time, to grip 'the xouter walls O'ftlle tubeto `hold the vlamb in axially adjusted '.posit'ion. Y Thus, for example,

ring H159 may have its upp`er halt externally' threaided and reduced in diameter. C irculnjerentiallyspaced axiallyextending'slots are formed in this Yreduced,portion/ two oi Whicliare diani'etrically oppo'sit'ely spaced to receive 4the elec-v,

trodes ofllainp l1,118. AInternally threaded ring I50` [is so io'rmedlthat When' it is screwed zonto ring llflin the position shown, .it caused the exible f portions of ringl, .that is, theportions between Vslots,v to clarnp the: tubel i115. Diametrically 013-.

'ipos'ite 'slotslii lintheWall of tube' |135, are pro# @seater j adjustment, 'and one or them. is enlarged at oneend suiiciently to enable the inlainplinto thentube. When it 'is he instrumentls: ,Constructed so v'thatfthecle"nthe actual projectile under investigation and '(2) the combined moment of the rotor, casing', gilnbal ring and force-applying cylinder and piston" about the transverse axis through the center of gravity kfolesired toi.axially'adjust'tliemlanrr ring |50 isr jllosened, 'thefadiustm'ent made'and maintained by re-'tighteningfthe ring. opqaue disc 152, f'having'a small cei'i`tral-ploolefl53 therein isheld' in the 'upper eed Of tube. .E it. eswi .be noted from Figure Ibi-i151@ @ed 01.30.1111@ .111 1S ',Clfosely' adiee't l thought-'sensitive record' sheetfi so that, When' lamp`-i'fi8`-ashes for al verybrief'periodLa spot l oflight is projected onto sheet i??? and when the I sheetv is ,dei/"e1op-ed',I appearsjas a. 4small y easily ndis- @1111111.11152 .dot Sieeliheshflamr audits C011- trol inet sl'iovvn. A ashrate offthe order of 30 times "per seconddwill 'be vrround generally satisfactory and. 'cante raredasldsd.

.Magnet .5, i andinductiori .coil 52, forming cornpnents of. 'thef means', yfor .determining theA speed oiv roto r38. have been; previously described. `'Ihesel parts are 'shown upon 'the circuit -iliagrarn of Figure 14 .1311@ teneilials' ef @hammamet l @bil .52., are. @heeded by'. .116.5111516 for .rie-.tail .C011- nections 4toafsoc'lfet A I 54' which ymaybelo.cated in .Q any erveriieetllbsition .911' theinsiiu'reeet .bese- ...Arlue ',l-fts' socket. ISA'-nl iS'QQmieciQed to' 'one :l y,end of; alengtli of :two -Wijre cable having plu g*Y I 5 I Aai-,wtsother encly ,forinsertion Vinto socket I'53,

the :leadsnfromivhich extendfintofamplil'e 'i 59. v :fr source of ,pfgyle IA. hC. power, T g'f'znerally .fidehtileat 150 supplies' a transjfefmer 211.151 fec- .Itiel 5 l. which! in. tejmupplies' plete voltage@ amplifier 15,0 anda ashlampIZ, which 'may 4be @G5131 Sirb'iehf ffu'sedto drive an"i00 P. M. synchronous motor "IEhh'aving a stroboscopic disc Iili' o riits shaft. l' Asshotthgt'ms disc'is' in 'ooitiontc te illuminated 4' by fla'rnpfl 62 ,r andv has a fplu'rality 'of concentric the appearsto be stationary. Under? this ,set-'un speeds" from '9000 lto 'about 30,000 vR', P'M. n'ay--b determined. Witlinterpolation, a. ttarqf 9Y dineren; speedstetween the twg 11mftsf naybe deter'fiied with reasonable accuracy.

'flem $0111?. bers of vdivisions rcuit .perfsefareWell'knovvn, the'lciijcuit is 'd Power source 50 is 'also' 'y of theassembly closely approximates the corre- `spending moment of the actual projectile. This j icankbel done by making the parts of metals of n diierent specic gravities, by varying 'thejsizes .of the component' parts and by their arrangement relatively to the axes concerned. It is 'conteinplated that one machine may sucelfor the testing of projectiles over a substantial range'of calibers.

(The instrumientv `shownis'a very versatile'one and numerous manners of conductingy 'test"'wi1l andcylinder 'E2 are in alignment in the plane of "bailfl, vvhichvplane islinclined at about 4567110 the vertical aboutaxis 23, as indicated byI the dotted lines at 7I'liciFigure l. Thebail 59 vis i `held inthis position by threaded shaft 80,"a'gainst thecentralizing action of spring IM. The valve, not shown, controlling theilow of air underpres- 'sure td air pipe I5 is'opened. Air under Ipres- 'sure then'floivs by Way of tube I4, tting I7, pipe V2I,` tting IBQ'ancl tubes E4 and 25, to chamber 3l', fror n whence it passes through j et orifices 33a, engagefpockets 39h in the `rotor and spin the Y s axne. Spentfair' emerges from 'the casing by lvfay of ports 53,'5 and IB? which are symmetri- Ically 'disposed so thatv net reaction force on the 'ca-'sing 'aboutr each pivot aids thereof, 'sl aero. Motor IEE is started and the amplifier I59'and 'transformer and. rectifier unity ISI, are'energized by' closing vsvitches '|65 and i166, Figure 14,' resoectively. 'Stroboscopic disc |611 is therebyil- With rotor 38. By yadjusting the air pressure valve', the 'rotorsneed may be brought to a'de'sired valuefwhich value 'is' attained when the radial "li'nesof the ring on disc It!! correspondingto the desirecl'speed, appears to be stationary. A sheet 'of vphotographic paper is positioned with its edges resting upon Aarcuate bars ISB vand '|39 and 'its 'ends are'clamped bythe mechanism 'described in connection With Figures 12 and 13.

With rotor 38 upto test'speed, motor' "18 an fla'sli'lanip M8 are energized. At 'this 'time the valve, v not shown, controlling the'application of Tnis v'alve is now iiuence'of their Irespective springs I I2 andIIS,

'are moved to thevrelease position shown upon g'fure 3. The valve, not showncontro'lling 4the per'fing'mayb' 'ts'ttted 'forum @atentar-.mor air pressure to cylinder 12l by way of flexible hose connected with nipple |68, Figure l, is now opened to urge the piston within cylinder 'I2 `and its rod 'I3 downwardly. The valve is so adjusted that the resulting force upon ball f|2a and the nose of the simulated shell, will closely approximate the resultant of vall the aerodynamic forces which act upon the actual projectile in night. This force may remain lconstant during a test without departing greatly from actual flight conditions. Or, if it is Idesired to more closely -represent actual flight conditions wherein the overturning moment decreases as the projectile approaches its vertex, ldue to decrease in velocity, the pressuremay be manually reduced to correspondingly decrease the thrust exerted by rod '|3. It is also contemplated that the valve may ybe controlled automatically during a test to simulate the condition of decreasing velocity.

Motor '|8 turns at constant speed and, in the manner previously described, swings bail 58 at the proper rate vabout its pivot axis 23. At the start of the test, the force exerted rby rod 'I3 upon the rotor casing, is in `alignment with the spin axis of the rotor and has no component transverse thereto, thereby correctly simulating the conditions extant as the real projectile leaves the muzzle of the gun; and should the simulated projectile continue to correctly follow the tangent to its trajectory, the rotor spin axis will remain in alignment with the rod 'H3 and the path dei-ined by the successive flashes of lamp |48, as recorded upon sheet |37, will `be an arcuate line intermediate the edges of the sheet `and with successive flash-dots spaced in a manner which can be predetermined merely by ruiming a test cycle with cylinder |2 clamped in position by members ||0 `and |1. This is the condition of no yaw, in which the Iprojectile strikes nose-foremost with its axis tangent to its trajectory.

In actual firing, where the projectile axis does not remain truly tangential to the trajectory, the resista-nce or force of the relative wind is no longer in alignment with the projectile axis. As a result, the force has a component tending to tilt or further deviate the projectile from a true tangential position. This component, acts, in accordance with well known gyroscopic action, to cause the projectile to precess or yaw in an elfort to place its spinning axis in alignment with the deviating component of external force. Since the axis of the deviating component always leads the precession axis by 901, as in the case of a spinning top, the result may be a wobble of the projectile nose of varying radius. All such erratic motions -of whatever type or nature, are accurately recorded on sheet |31 and, in the case of component movements about axis 3| are proportional to the deviation of the corresponding dot from the median line of the sheet, while components about axis 23 are proportional to the amounts by which the respective dots lead or lag the corresponding dots of a standard or perfect graph. Since the time of a test is known and is equal to the time of flight of the actual projectile whose characteristics are being investigated, the position of the shell axis at any time relatively to the instantaneous tangent t its trajectory can be readily determined, as well as the rates of yaw and deviation. In short, the major ballistic characteristics of the actual projectile under investigation can be determined and the effects of various changes in construction yof the projectile, as well as the effects of changes in gun rifling and powder charge, accurately evaluated. Other uses for the instrument will readilyocc-ur t0 those skilled in vable by-pass switches are connected in parallel with each of the microswitches 99 and |80 so that motor 18 can be started despite the fact that one microswitch is open at the beginning of a test.

vThe extreme positions of projector tube H55 at the beginning and end of a test, are indicated at |450 and |45d, Figure 1. Angular movement during a test may be in either direction. The limiting transverse positions of the recorder tube M5 during a, test, are indicated in dotted lines at |l5a and |451), Figure 3,` and are ample to accommodate the maximum yaw encountered in actual practice.

While I have shown the presently preferred form of the invention, numerous modications, refinements and substitutions will occur to those skilled in the art after having studied the disclosure, Therefore I desire and intend that the present showing be taken in an illustrative rather than a limiting sense; and I wish to reserve all those modifications falling within the scope of the subjoined claims.

Having now fully disclosed the invention, what I claim and desire to secure by Letters Patent is:

1. In a ballistics testing machine, a rotor simulating in size, shape, and moments of inertia, an actual projectile whose characteristics in flight are to be determined, means mounting said rotor for universal pivotal movement about horizontal axes through its center of gravity, means for spinning said rotor about its longitudinal axis, and means operable to apply a known force having a component parallel to said longitudinal axis, to said rotor at a point on said axis forwardly of said center of gravity.

2. A testing machine as recited in claim 1, and means to move said force applying means to vary at a known rate the angular relation between the line of action of the force exerted thereby and the longitudinal spin axis of said rotor.

3. A testing machine as recited in claim 2, means including a magnet fixed to said rotor to determine the speed of spinning thereof, and means to record. the movement of the line of action yof the force applied by said force applying means.

4. In a machine for investigating the performance of projectiles, a casing, a simulated projectile having a longitudinal axis and also having substantially the same size, shape, mass, and moments as those of an actual projectile under investigation, means mounting said simulated projectile in said casing for spinning about the longitudinal axis thereof, means carried by said casing for so spinning said simulated projectile,

- means operable to apply a force to said casing having a component parallel with said axis, and means to angularly vary at a known rate, the direction of said force.

5. In a ballistics testing instrument, a, frame, a casing, a gimbal ring mounting said casing on said frame for universal angular movement, a simulated projectile having a longitudinal axis of symmetry and mounted in said casing for spinning about its longitudinal axis iixed with respect to said casing, cooperating means between said casing and projectile for spinning the latter about ment thereof.

17. A ballistics testing machine comprising a base, a simulated projectile having known ballistic characteristics representative of those of an actual projectile whose ballistics are to be determined, a hollow gimbal ring, hollow outer trunnions mounting said ring on said base for pivotal movement about a irst diametral axis of said ring, a casing, hollow inner trunnions mounting said casing in said ring for pivotal movement about a second diametral axis of said ring normal to said rst axis, means journaling said projectile in said casing for spinning about its longitudinal axis normal to said second axis, all said axes being concurrent at the center of gravity of the combined projectile and casing, air turbine means carried by said projectile and comprising a rst and second series of circumferentially spaced air pockets, the pockets of one series being axially spaced and oppositely directed from those of the rst series, means carried by said casing for forming rst jets impinging said rst series of pockets to spin said projectile in one direction, means carried by said casing for forming second jets impinging said second series of pockets to spin said projectile in the opposite direction, there being a first air passage to said rst jets through one 4each of said outor and inner trunnions and a portion of said ring, there being a second air passage to said second jets through the other of said outer and inner trunnions and another portion of said ring, said passages being separate and distinct.

18. A machine as recited in claim 17, a bail pivoted on said base for independent pivotal movement about said first diametral axis in the plane of said ring, said iirst diametral axis being horizontal, resilient means urging said bail into vertical position, an air cylinder, gimbal ring means mounting said cylinder on said bail for universal movement on said bail about a rst point above said first diametral axis, a piston in said cylinder, a rod depending from said piston, and universal contact means between said rod and casing at a second point on said longitudinal axis, said second point being between said first point and iirst diametral axis.

19. A machine as recited in claim 18, a light projector including a iiash lamp carried by said air cylinder to project a beam of light parallel with said cylinder and means for supporting a photographic record strip coaxial of said first diametral axis and in closely adjacent relation with said light projector.

ROBERT L. PIGFORD.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,560,435 Sperry Nov. 3, 1925 2,327,515 Ferrone et al. Aug. 24, 1943 2,353,150 Dietz July 11, 1944 2,373,024 Gunn et al Apr. 3, 1945 2,423,831 Garbarini et al July 115, 1947 2,440,968 Moore et al May 4, 1948 2,470,773 Haskins May 24, 1949 2,490,574 Austin .Dec. 6, 1949 

